0

Update on Nutrient, Benthic Algal levels and Aquatic Fauna

in the Russell River and their relationship to discharges from the

Huon Aquaculture Company (HAC) farm facility

Report to Huon Aquaculture Company

June 2015

Peter Davies

FFrreesshhwwaatteerr

SSyysstteemmss AAqquuaattiicc EEnnvviirroonnmmeennttaall CCoonnssuullttiinngg SSeerrvviiccee

82 Waimea Ave, Sandy Bay, Tasmania Australia 7005

Ph/Fax: 03 62254660

p.e.davies@utas.edu.au

1

Contents

Background ................................................................................................................................... 2

Methods ........................................................................................................................................ 3

Study sites ................................................................................................................................. 3

Water quality ............................................................................................................................. 3

Benthic Algae ............................................................................................................................. 3

Benthic invertebrates ................................................................................................................ 5

Fish ............................................................................................................................................ 5

Flow data ................................................................................................................................... 5

Results ........................................................................................................................................... 6

Farm Biomass and Feed rates .................................................................................................... 6

Feed limits ................................................................................................................................. 7

Flows ......................................................................................................................................... 9

Nutrients ................................................................................................................................... 9

Feed nutrient content .............................................................................................................. 20

Benthic algae ........................................................................................................................... 21

Algal-nutrient relationships and thresholds .............................................................................. 29

Relationships with farm stock and feed rates ........................................................................... 31

Benthic invertebrates .............................................................................................................. 32

Fish .......................................................................................................................................... 38

Discussion ................................................................................................................................... 39

References .................................................................................................................................. 41

2

Background This report provides an update on the water quality and benthic (bottom-dwelling) algal study of the

Russell River conducted for the Huon Aquaculture Company (HAC) by Peter Davies of Freshwater

Systems and Dom O’Brien of Aquaculture, Management & Development P/L. This report builds on

the work reported in the original 2009 report, which made several recommendations with regard to

monitoring and limiting feed rates in the flow-through ponds at the HAC site.

The original 2009 report aimed to:

describe conditions in the river;

assess the relationships between nutrient levels and benthic algal levels in the Russell;

assess the degree of influence of the HAC facility on the algal levels;

identify any thresholds in algal and nutrient levels which may be used in management to

improve the environmental outcomes in the river; and

assess any relationships between nutrient levels and feed or stocking rates in the HAC farm.

This report describes the results of sampling conducted since late 2009 and:

re-examines relationships between algal levels, nutrients and feed rates in the Russell at two

locations:

o Site 5 – in the reach downstream of the HAC outfall; and

o Site 7 – at Lorkin’s Bridge, 3 km downstream of the outfall;

re-evaluates the condition of benthic macroinvertebrate and fish assemblages in the Russell;

assesses the success of HAC’s algal management to date.

Several subsidiary issues are also examined, though not exhaustively:

the influence of a period of increase in phosphorus in brood stock diets used in the ponds at

the HAC site between May 2014 and November 2014 on nutrient levels in the outfall and

river;

the controls of algal levels in the Russell other than the HAC outfall.

3

Methods

Study sites

Eight sites have been used in the Russell River for sampling of water quality and benthic algae as

shown in Figure 1. Three sites were upstream of the HAC farm intake (sites 1 to 3). One site was

located downstream of the first farm outfall (site 4) and another downstream of the second, main

farm outfall (site 5). The remaining 3 sites were located at increasing distances downstream. Site

locations and distances from the upper bridge are shown below (Table 1).

Four sites, sites 1, 3, 5 and 7, have been sampled routinely since late 2009 (Table 1) and the majority

of the results and analyses reported in this document relate to these four sites.

Water quality

Water quality was sampled at the four routine sampling sites site on between 31 and 37 occasions

between August 2009 and March 2015.

On each occasion water samples were analysed for Total Nitrogen (TN), Ammonia (NH4), Nitrate +

Nitrite, (NOx), pH, Total Phosphorus (TP), Dissolved Reactive Phosphorus (DRP), total suspended

solids (TSS) , conductivity and turbidity. Water samples were analysed by the Hobart laboratories of

Analytical Services Tasmania (AST).

Benthic Algae

River bottom (benthic) algae were assessed on the majority (34) of these occasions (when river

levels allowed safe access to the stream bed).

Benthic algal biomass was assessed at each site by sampling of 15 upper rock (cobble) surfaces with

a scourer pad sampler (method of Davies and Gee 1993), with sample locations situated randomly

across the channel in rocky bed (riffle) habitat. Scourer pad samples were extracted using an

acetone-methanol solution and analysed colorimetrically for chlorophyll-a content using a visual

wavelength spectrophotometer, by a standard method (consistent with APHA Standard Methods

2005). Chlorophyll-a values were corrected to mg per unit area (mg/m2) values and used as a

surrogate for algal biomass.

In addition, benthic algal cover was assessed quantitatively at each site, by visual assessment using a

100 cell 30 x 30 cm gridded quadrat, placed on the stream bed at 5 random locations across the

channel, again in riffle habitat.

Algal cover was assessed on 34 occasions between August 2009 and March 2015, and algal biomass

(as chlorophyll-a per unit area) was assessed on 24 occasions

4

Table 1 Location of sampling sites and distance from upper Lonnavale Road – Russell Road Bridge

(Grid references in GDA datum). Sites underlined and in italics have been routinely monitored

since late 2009.

Site Description Distance from upper bridge (km) Easting Northing

1 At Russell Rd bridge 0 482707 5245644

2 Above offtake 1 482825 5245297

3 Above offtake 2 483128 5245311

4 Below 1st outlet 2.5 483382 5245085

5 Below main outlet 3 483781 5245024

6 Above Lorkins Bridge 3.5 484138 5244766

7 Lorkins Rd bridge 4 485638 5243505

8 Lonnavale Rd bridge 8 488615 5240871

1

2 3

4 5

6

7

8

Figure 1. Map of sampling locations (1 – 8). HAC farm outfalls indicated by black arrows. Map is at

1:25000 scale, with 1 km grid squares.

5

Benthic invertebrates

Benthic invertebrates were sampled on two occasions in spring (November) 2014 and autumn

(March) 2015, using the standard AUSRIVAS rapid assessment protocol. Riffle habitats were sampled

using standard kick net and live-pick protocol, with all benthic invertebrates identified to family

level. Data was analysed using the DPIPWE AUSRIVAS autumn season riffle habitat model to

generate an O/E (observed to expected ratio) score for each site. It was also used to derive an ‘EPT’

score – an indicator based on the proportion of taxa from the orders of aquatic insects

Ephemeroptera, Plecoptera and Trichoptera – known to be sensitive to organic pollution.

Fish

Fish were quantitatively sampled twice, once in spring (November) 2014 and autumn (March) 2015,

by electrofishing for a standard 1200 seconds of battery ‘on-time’, searching all instream habitats.

All fish captured were identified and released.

Flow data

Flow data were collected from a gauging station (with automatic stage recorder and gauge board)

established at Lorkins Bridge in the Russell River. Water level (stage) was recorded at 15 minute

intervals, and related to river discharge by periodic manual flow gauging. This was used to derive a

time series of flow in the Russell.

These flow data were used to estimate instantaneous nutrient loads in the Russell on the days of

water quality sampling.

6

Results

Farm Biomass and Feed rates

Plots of monthly total fish biomass, numbers and feed rates in the HAC flow-through pond system

are shown in Figures 2 and 3 for the entire period of this study from January 2008. Biomass and

numbers were reduced substantially in November 2008, with a consequent reduction in feed input.

Biomass was gradually increased from that date to reach 6,000 to 7,500 kg between late 2011 and

late 2014, followed by a slight reduction to April 2015. It should be noted that HAC have indicated

that they will be capping their stocking level in future at 4,500 broodstock in the flow-through

ponds.

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10,000

20,000

30,000

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60,000

Jan-04 May-05 Oct-06 Feb-08 Jul-09 Nov-10 Apr-12 Aug-13 Dec-14 May-16

Biomass (kg)

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600,000

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Numbers

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1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

Feb-08 Jul-09 Nov-10 Apr-12 Aug-13 Dec-14 May-16

Figure 2. Trends in total fish biomass and numbers in the HAC flow-through pond system from

January 2008 to April 2015. Bottom plot inset shows trend in numbers following the major

reduction in November 2008.

7

Feed limits

An overall monthly feed input limit of between 800 and 1,000 kg was proposed by Davies (2009), on a trial basis, under the current farm water management arrangement, to attempt to minimise risk of high algal levels. From the beginning of 2009 monthly feed inputs fluctuated widely, and periodically reached or exceeded the recommended 1,000 kg provisional limit proposed by Davies (2009), especially from July 2012 to December 2013. The lower risk threshold of 800 kg was exceeded occasionally from November 2008 to December 2012 and then for most of the time after that. A higher phosphorus (‘High Nutrient’) feed was used in the pond system between May 2014 and

November 2014, indicated in Figure 3. Feed nutrient content was returned to normal levels after

that period. It was a high nutrient feed specifically designed for broodstock health and well-being.

Part of the nutrient increase included an increase in phosphorus content. Once this was realised by

HAC, the phosphorus content was reduced (HAC pers. comm.).

There had been a strong relationship between feed input and biomass in the HAC pond facility prior

to 2008 (Figure 4). Following the reduction in feed inputs from 2008 on, and for the duration of this

study, feed inputs were much lower than previously and the feed-biomass relationship was much

weaker.

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2,000

4,000

6,000

8,000

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Jan-04 May-05 Oct-06 Feb-08 Jul-09 Nov-10 Apr-12 Aug-13 Dec-14 May-16

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1,000

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Oct-06 Feb-08 Jul-09 Nov-10 Apr-12 Aug-13 Dec-14 May-16

Feed (kg)High PFeed

8

Figure 3. Trends in total monthly feed supplied to the HAC flow-through pond system from

October 2005 to April 2015 (top plot). Bottom plot is from January 2008 only, with the period of

‘High phosphorus’ feed indicated. The horizontal lines indicate the initial 1000 kg monthly feed

limit proposed by Davies (2009), and the lower risk 800 kg limit.

R² = 0.7668

-

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

- 10,000 20,000 30,000 40,000 50,000 60,000

Fee

d (

kg)

Biomass (kg)

Oct 2005 to Dec 2007

Jan 2008 to Apr 2015

Figure 4. Relationship between total monthly feed supplied to the HAC flow-through pond system

and fish biomass from October 2005 to December 2007 and from January 2008 to April 2015 (the

period of this monitoring study). Linear relationship and r2 value shown for the first period.

9

Flows

The full record of flow data from the gauging station at Lorkins Bridge is shown in Figure 5. Most years showed a similar seasonal pattern, with drier conditions persisting in 2014 punctuated by higher flow events, higher seasonal baseflows persisting in winter-spring of 2009 and 2013, and high flows (> 30 cumec) events observed particularly in 2011, 2013 and 2014 when a single extreme event occurred (83 cumec on 31 July 2014).

Nutrients

Plots of nutrient values at each site in the Russell are shown across all sampling occasions from 2008 to 2015 in Figures 6 to 10. Concentrations of TP, NH4 and DRP are higher at sites 5 and 7 overall than at sites 1 and 3, throughout the entire study period from 2008 to 2015. A similar general pattern occurs for TN though less consistently, while NO3 levels are only occasionally raised at the downstream sites relative to sites 1 and 3. A transient decline in NH4, NO3 and Total P was observed at site 5 in late 2008 early 2009 following reduction in feed inputs in the HAC flow-through ponds. However the general pattern of higher nutrient concentrations at site 5 returned and remained in place (though with considerable variation) until 2015. NH4 levels have risen to particularly high levels (similar to the peak observed in early 2008) at site 5 since 2012. NH4, NO3, TP and DRP levels were consistently higher at site 5 than at site 7 throughout the monitoring record, with the exception of occasions in 2010 to 2012 when TN and NH4 levels at site 7 exceeded those at site 5. Generally, nutrient levels continued to be raised above base levels at site 5 downstream of the HAC farm outfalls, with a decline in a downstream direction falling toward, though often not equating to, values observed upstream of the farm intake. Figures 11 and 12 illustrate the difference between concentrations at site 5 and site 1, as well as at site 7 and site 1. Values for both sites tend to be mainly positive (i.e. higher than at site 1) on the same sampling date. The majority of these difference values tend to be higher for site 5 than site 7. It should be noted that zero values in these figures occur when concentrations are not different OR when both concentrations fell below the analytical detection reporting limit. Only on rare occasions (2 to 4 samples out of 40), does site 7 have higher concentrations relative to site 1 than site 5, or has concentrations that are significantly lower than at site 1 (i.e. negative values in Figures 11 and 12). Highly bioavailable forms of nutrients (DRP, NH4 and NOx) at site 7 were not significantly higher than at site 1 (the overall means of these differences being of 0.000413, 0.0008 and 0.000175 mg/l respectively). To further illustrate this, of the 40 samples in the data set 8 and 6 (20 and 15%) had DRP concentrations at site 7 that were higher and lower, respectively, than at site 1 (the majority of which by only 0.001 mg/l). 6 and 1 of these respective occasions occurred at the same time as at site 5. Correlations between nutrient concentration values at sites 7 and 5 and those at site 1 are shown in Figure 13. Nutrient concentrations are unambiguously higher on most occasions at site 5 than at site 1, with the exception of total nitrogen where levels fall close to those at site 1 when TN levels are high. Total nitrogen is strongly correlated with those at site 1 for both sites 7 and 5 (Figure 13), while ammonia and NOx concentrations are substantially higher at site 5 than ait site 1 on most occasions. This difference in relationships between soluble and total nitrogen forms is expected, since NOx and NH4 are only a small proportion of total nitrogen – much of which is in organically bound particulate

10

form and with concentrations dictated by transport of this material through the river system (as opposed to delivered by the HAC outfall). High TN level are likely to be dictated by high flow related transport of particulate N through the river system. DRP concentrations at site 5 are higher overall than at site 1 and fall above the 1:1 line (Figure 13). This is not the case for site 7, for which the relationship with site 1 concentrations generally falls close to the 1:1 line. It therefore appears that any elevated DRP observed at site 5 is absorbed to background concentrations by the time site 7 is reached. This suggests that DRP sourced from the HAC outfall is unlikely to regularly drive algal changes at site 7. In contrast to TN, TP is generally elevated above site 1 levels at site 5, and this pattern is partially reflected at site 7. These results suggest that nutrient levels at site 7 are partially influenced by events that drive the elevated nutrient concentrations observed at site 5. This site is also influenced by nutrient inputs other than those influencing site 5, i.e. other than the HAC outfall.

11

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Flo

w a

t Lo

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s B

rid

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cum

ec)

Figure 5. Flows at Lorkins Bridge from late 2008 to early 2015

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Russell 5 Russell 7

Figure 6. Total-N concentrations at Russell River sites 1, 3, 5 and 7 between March 2008 and March

2015.

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NH

4 (

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Russell 5 Russell 7

Figure 7. Ammonia-N concentrations at Russell River sites 1, 3, 5 and 7 between March 2008 and

March 2015.

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Russell 5 Russell 7

Figure 8. Nitrate-N concentrations at Russell River sites 1, 3, 5 and 7 between March 2008 and

March 2015.

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(m

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Russell 5 Russell 7

Figure 9. Total-P concentrations at Russell River sites 1, 3, 5 and 7 between March 2008 and March

2015.

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P (

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Russell 5 Russell 7

Figure 10. Dissolved Reactive-P (DRP) concentrations at Russell River sites 1, 3, 5 and 7 between

March 2008 and March 2015.

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Dif

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Russell 5 Russell 7

Figure 11. Differences in Total Nitrogen and Phosphorus concentrations between Russell River site

5 and 1, and between site 7 and 1 between March 2008 and March 2015. A positive value

indicates that the concentration at the site 5 or 7 is greater than at site 1.

18

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03/1

0

06/1

0

09/1

0

12/1

0

03/1

1

06

/11

09/1

1

12/1

1

03

/12

06/1

2

09/1

2

12/1

2

03/1

3

06/1

3

09/1

3

12/1

3

03/1

4

06/1

4

09

/14

12/1

4

03/1

5

DR

P D

iffe

ren

ce (

mg/l

)

Russell 5 Russell 7

-0.015

-0.010

-0.005

0.000

0.005

0.010

0.015

0.020

0.025

12/0

7

03/0

8

06/0

8

09/0

8

12

/08

03/0

9

06/0

9

09/0

9

12/0

9

03/1

0

06/1

0

09/1

0

12/1

0

03/1

1

06

/11

09/1

1

12/1

1

03

/12

06/1

2

09/1

2

12/1

2

03/1

3

06/1

3

09/1

3

12/1

3

03/1

4

06/1

4

09

/14

12/1

4

03/1

5

NH

4 D

iffe

ren

ce (

mg/l

)

Russell 5 Russell 7

Figure 12. Differences in Dissolved Reactive Phosphorus and Ammonia concentrations between

Russell River site 5 and 1, and between site 7 and 1 between March 2008 and March 2015. A

positive value indicates that the concentration at the site 5 or 7 is greater than at site 1.

19

R² = 0.22870

0.005

0.01

0.015

0.02

0.025

0 0.005 0.01 0.015 0.02 0.025

Site

7

Site 1

NH4

R² = 0.00210

0.005

0.01

0.015

0.02

0.025

0 0.005 0.01 0.015 0.02 0.025

Site

5

Site 1

NH4

R² = 0.11270

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0 0.005 0.01 0.015 0.02

Site

7

Site 1

Nox

R² = 0.00010

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0 0.005 0.01 0.015 0.02

Site

5

Site 1

Nox

R² = 0.55210

0.05

0.1

0.15

0.2

0.25

0 0.05 0.1 0.15 0.2 0.25

Site

7

Site 1

TN

R² = 0.53620

0.05

0.1

0.15

0.2

0.25

0 0.05 0.1 0.15 0.2 0.25

Site

5

Site 1

TN

R² = 0.75990

0.002

0.004

0.006

0.008

0.01

0.012

0 0.002 0.004 0.006 0.008 0.01 0.012

Site

7

Site 1

DRP

R² = 0.65670

0.002

0.004

0.006

0.008

0.01

0.012

0 0.002 0.004 0.006 0.008 0.01 0.012

Site

5

Site 1

DRP

R² = 0.01290

0.005

0.01

0.015

0.02

0 0.005 0.01 0.015 0.02

Site

7

Site 1

TP

R² = 0.04620

0.005

0.01

0.015

0.02

0 0.005 0.01 0.015 0.02

Site

5

Site 1

TP

Figure 13. Relationships between concentrations of nutrients at sites 7 and 5 and those at site 1.

Linear regression and r2 values shown. Dashed line = 1:1 relationship.

20

Feed nutrient content

The relationship between DRP levels in the outflow and the monthly feed input show that DRP levels were highest per unit feed during the Higher P feed period (Figure 14). In addition, the difference in DRP load per unit time in the Russell between site 5 and site 3 was greatest per unit feed input during the High P feed period (Figure 15). These results indicate that feeding with Higher P feed caused higher levels of DRP to be lost to the HAC waste stream and to the river than with normal feed.

0.000

0.005

0.010

0.015

0.020

0 200 400 600 800 1000 1200 1400 1600

Ou

tflo

w D

RP

(m

g/l)

Normal Feed

High P Feed

Figure 14. DRP in HAC wastewater outflow vs monthly feed input, with samples from the period of

‘High P’ feed highlighted.

R² = 0.3188

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 200 400 600 800 1000 1200 1400

DR

P lo

ad d

iffe

ren

ce (

kg/d

ay)

Feed (kg)

Normal Feed

High P Feed

Figure 15. DRP load contributed by HAC wastewater in the Russell River at site 5 vs monthly feed

input, with samples from the period of ‘High P’ feed highlighted.

21

Benthic algae

Both benthic algal biomass, as indicated by chlorophyll-a (chl-a) levels, and % cover of the river bed have remained markedly elevated downstream of the HAC outfalls throughout the entire study period (Figures 16 to 19). A marked rise in chl-a level was observed downstream of the HAC outfalls at site 5 throughout the sampling program, partially declining at site 7. On no occasion was the chl-a level at site 5 lower or equal to that observed at the upstream site 3. On only rare occasions was % algal cover at site 5 lower than at site 3 (4 out of 34 occasions). This occurred more frequently at site 7 where on 13 out of 34 sampling occasions, algal cover was equal to or lower than at site 3. Overall, there is a major change in mean and median algal biomass and cover at site 5, the pattern of which was broadly similar for three annual time periods selected to cover the same seasonal sequence (Figures 18 and 19). These levels remain high, with annual mean % algal cover often exceeding 30% and frequently 50-60% of the stream bed. Reductions in mean algal chlorophyll and % cover levels were observed at site 5 over the sampling program (Figures 18 and 19). By contrast, an increase in mean algal chlorophyll levels and % cover was observed at site 7 in 2014-15. The pattern is only slightly different when median values are considered. Chlorophyll-a levels are highly correlated between site 1 and 3, indicating that they are responding to similar environmental cues (Figure 20). This relationship explains some 40% of the variance in the data. Chlorophyll-a levels at site 7 are also correlated with those at sites 1 and 3, but not with those at site 5 (Figure 20). This suggests that chl-a level at site 7 is at least partially controlled by drivers of change unrelated to the HAC discharge. This is reinforced in the plots of change in chl-a between sampling occasions (Figure 22) where changes at site 3 explain some 25% of the variance in changes at site 7, in contrast to site where changes in chl-a explain only 7% of the variance at site 7. Chl-a levels at site 5 are not correlated with those at sites 3 or 1 (Figure 21), indicating that temporal changes in chl-a at this site continue to be driven by other factors (e.g. elevated nutrient input from the HAC outfall). By contrast, % algal cover at site 7 is strongly related to that at site 5 (Figure 23), and changes in cover with time are also correlated between these two sites (Figure 24). In addition, algal cover levels at site 7 are frequently higher than those observed at site 5 and this has occurred throughout the period of study. These results suggest that biomass (as chl-a) is driven by a combination of factors with no relation to the HAC discharge, while % cover is strongly driven by the influence of the HAC outfall with some other possible additional influence (e.g. nutrient source).

22

0

20

40

60

80

100

120

12/0

7

03/0

8

06/0

8

09/0

8

12/0

8

03/0

9

06/0

9

09/0

9

12/0

9

03

/10

06/1

0

09/1

0

12

/10

03/1

1

06/1

1

09

/11

12/1

1

03/1

2

06/1

2

09/1

2

12/1

2

03/1

3

06/1

3

09/1

3

12/1

3

03/1

4

06/1

4

09/1

4

12

/14

03/1

5

Chl-

a (m

g/m

2)

Russel 1 Russel 3

0

20

40

60

80

100

120

12/0

7

03/0

8

06/0

8

09/0

8

12/0

8

03/0

9

06/0

9

09/0

9

12/0

9

03

/10

06/1

0

09/1

0

12

/10

03/1

1

06/1

1

09

/11

12/1

1

03/1

2

06/1

2

09/1

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12/1

2

03/1

3

06/1

3

09/1

3

12/1

3

03/1

4

06/1

4

09/1

4

12

/14

03/1

5

Chl-

a (m

g/m

2)

Russel 5 Russel 7

Figure 16. Benthic algal chlorophyll-a values at Russell River sites 1, 3, 5 and 7 between March

2008 and March 2015.

23

0

20

40

60

80

100

12

/07

03/0

8

06/0

8

09/0

8

12/0

8

03/0

9

06/0

9

09/0

9

12/0

9

03/1

0

06

/10

09/1

0

12/1

0

03/1

1

06/1

1

09/1

1

12/1

1

03/1

2

06/1

2

09/1

2

12/1

2

03/1

3

06/1

3

09

/13

12/1

3

03/1

4

06/1

4

09/1

4

12/1

4

03/1

5

% A

lgal

Cov

er

Russell 1 Russell 3

0

20

40

60

80

100

12/0

7

03/0

8

06/0

8

09/0

8

12/0

8

03

/09

06/0

9

09/0

9

12

/09

03/1

0

06/1

0

09/1

0

12/1

0

03/1

1

06/1

1

09/1

1

12/1

1

03/1

2

06/1

2

09/1

2

12/1

2

03/1

3

06/1

3

09/1

3

12

/13

03/1

4

06/1

4

09

/14

12/1

4

03/1

5

% A

lgal

Cover

Russell 5 Russell 7

Figure 17. Benthic algal cover values at Russell River sites 1, 3, 5 and 7 between March 2008 and

March 2015.

24

0

10

20

30

40

50

60

Russel 1 Russel 3 Russel 5 Russel 7

Me

an C

hlo

rop

hyl

l-a

(mg/

m2)

03/08 to 05/09 02/12 to 05/13 03/14 to 05/15

Means

0

10

20

30

40

50

60

Russel 1 Russel 3 Russel 5 Russel 7

Me

an C

hlo

rop

hyl

l-a

(mg/

m2)

03/08 to 05/09 02/12 to 05/13 03/14 to 05/15

Medians

Figure 18. Mean and median values of benthic algal Chlorophyll-a (mg/m2) for each site from three

similar seasonal time periods between 2008 and 2015, showing marginal decline at site 5 and

increase at site 7. Dashed lines indicate high and low thresholds developed by Davies (2009) for

mean chlorophyll-a.

25

0

10

20

30

40

50

60

70

Russel 1 Russel 3 Russel 5 Russel 7

Me

an %

Alg

al C

ove

r

03/08 to 05/09 02/12 to 05/13 03/14 to 05/15

Means

0

10

20

30

40

50

60

70

Russel 1 Russel 3 Russel 5 Russel 7

Me

an %

Alg

al C

ove

r

03/08 to 05/09 02/12 to 05/13 03/14 to 05/15

Medians

Figure 19. Mean and median values of % benthic algal cover for each site from three similar

seasonal time periods between 2008 and 21015, showing marginal decline at site 5 and increase at

site 7. Dashed lines indicate high and low thresholds developed by Davies (2009) for mean cover.

26

R² = 0.4117

0

5

10

15

20

25

30

35

0 5 10 15 20 25

Ch

la R

uss

el s

ite

3

Chla Russel site 1

R² = 0.299

0

10

20

30

40

50

60

70

0 5 10 15 20 25 30 35

Ch

la R

uss

el s

ite

7

Chla Russel site 3 R² = 0.3046

0

10

20

30

40

50

60

70

0 5 10 15 20 25

Ch

la R

uss

el s

ite

7

Chla Russel site 1 R² = 0.1696

0

10

20

30

40

50

60

70

0 20 40 60 80 100 120

Ch

la R

uss

el s

ite

7

Chla Russel site 5

Figure 20. Relationships between benthic algal chlorophyll-a values (mg/m2) at sites 7, 5, 3 and 1

across the entire study period from March 2008 to March 2015. Linear trend r2 values shown.

27

R² = 0.0633

0

20

40

60

80

100

120

0 5 10 15 20 25 30 35

Ch

la R

uss

el s

ite

5

Chla Russel site 3

Figure 21. Relationship between benthic algal chlorophyll-a values (mg/m2) at site 5 and 3 across

the entire study period from March 2008 to March 2015. Linear trend r2 value shown.

R² = 0.0734

-50

-40

-30

-20

-10

0

10

20

30

40

50

60

-100 -50 0 50 100

Ch

ange

in C

hla

at

site

7

Change in Chla at site 5

R² = 0.2493

-50

-40

-30

-20

-10

0

10

20

30

40

50

60

-20 -15 -10 -5 0 5 10 15 20 25

Ch

ange

in C

hla

at

site

7

Change in Chla at site 3

Figure 22. Relationships of changes in benthic algal chlorophyll-a values (mg/m2) between

consecutive sampling events for sites 7 and 5, and for sites 7 and 3 across the entire study period

from March 2008 to March 2015. Linear trend r2 values shown.

28

R² = 0.3880

20

40

60

80

100

0 20 40 60 80 100

% a

lgal

co

ver

at R

uss

el s

ite

7

% algal cover at Russel site 5

Figure 23. Relationship between % benthic algal cover at site 7 and 5 across the entire study

period from March 2008 to March 2015. Curvilinear trend r2 value shown.

R² = 0.2905-60

-40

-20

0

20

40

60

80

100

-80 -60 -40 -20 0 20 40 60 80 100

Ch

ange

in %

alg

al c

ove

r at

sit

e 7

Change in % algal cover at site 5

Figure 24. Relationship of change in benthic algal cover between consecutive sampling events

across sites 7 and 5 for the entire study period from March 2008 to March 2015. Linear trend r2

values shown.

29

Algal-nutrient relationships and thresholds

Relationships of chlorophyll-a and % cover with TP across the Russell River sites were highly significant and linear for the entire period from 2008 to 2015 (Figure 25). This was also the case for TN, though the relationship was observed to transiently shift during the period February 2012 to May 2013. A very steep relationship is observed by between averaged chl-a and % cover levels even at low concentrations of P and N in the Russell (Figure 25). These relationships were re-evaluated for this report using the entire 2008 to 2015 data set, and can be seen to be broadly similar for the three time periods compared in Figure 22, with no indication of any substantial change. Local nutrient thresholds were established for the Russell River in the previous report (Davies 2009). Algal thresholds (for chl-a and % cover) were first selected for the Russell River in order to identify the nutrient thresholds. Davies (2009) then determined nutrient threshold values below which algal levels have a low risk of exceeding the algal thresholds. Davies (2009) proposed a 30 mg/m2 annual mean value as a reasonable interim chlorophyll-a

management threshold, accepting a mild impact with the risk of occasional higher algal levels

downstream of the farm, and taking into account the variability of algal biomass in the upstream

reference sites. Davies (2009) then examined the Chl-a – nutrient concentration relationships and

the 30 mg/m2 chl-a threshold was then equated to derive mean water quality thresholds in the

Russell River immediately downstream of the discharge (site 5) as follows:

TN 0.065 mg/l NOx 0.012 mg/l NH4 0.0035 mg/l TP 0.005 mg/l (0.007 mg/l in Nov-May, 0.0045 mg/l in Jun-Oct) DRP 0.003 mg/l The use of these Russell River nutrient thresholds was proposed as an interim management thresholds to be applied during an evaluation period leading up to this present report1. Examination for the relationships in Figure 25, where the thresholds are shown for annual mean Chl-a, % cover and TN and TP, show that they have been consistently exceeded at sites 5 and 7 throughout the sampling program (with the exception of the higher risk 60 % cover threshold).

1 These thresholds to be applied as differences between values measured at site 5 and at the farm intake (site

3), estimated as means over a 12 month period. This allows for variation in background nutrient levels, as well

as statistical uncertainty in the relationship between algal biomass and nutrient concentrations.

30

0

10

20

30

40

50

60

0.0000 0.0025 0.0050 0.0075 0.0100

Ch

l-a

(mg/

m2

)

TP (mg/l)

03/08 to 05/09

02/12 to 05/13

03/14 to 05/15

0

10

20

30

40

50

60

0.00 0.03 0.05 0.08 0.10 0.13

Ch

l-a

(mg/

m2

)

TN (mg/l)

03/08 to 05/09

02/12 to 05/13

03/14 to 05/15

0

10

20

30

40

50

60

70

80

0.000 0.005 0.010

% c

ove

r

TP (mg/l)

03/08 to 05/09

02/12 to 05/13

03/14 to 05/15

Figure 25. Relationships of average Chlorophyll-a levels (top two plots) and % algal cover (bottom

plot) with average total P and N concentrations for sites 1, 3, 5 and 7 for three comparable time

periods over the span of this study. Boxes indicate the ideal threshold limits originally identified

by Davies (2009). Point for site 6 also added for 03/08 to 05 09 period.

31

Relationships with farm stock and feed inputs

No significant relationship could be established between chl-a or % cover levels at site 5 in the Russell and the feed input in the month of sampling, or for the two months prior to sampling (Figure 26). Similar results were obtained when the feed input was averaged for up to 4 months prior to the sampling event. DRP levels in both the HAC outflow discharge and the Russell at site 5 were however strongly correlated with both the feed input and the feed nutrient quality (see above, Figures 11 and 12). These results suggest that algal chlorophyll-a and % cover levels at both sites 5 and 7 have not been directly driven by levels of feed input to the farm during the months immediately preceding the algal sampling, when considered over the entire study period from 2008 to 2015.

0

20

40

60

80

100

120

0 500 1000 1500 2000

Ch

l-a

Ru

sse

ll si

te 5

(m

g/m

2)

Feed (kg/month)

0

10

20

30

40

50

60

70

0 500 1000 1500 2000

Ch

l-a

Ru

sse

ll si

te 7

(m

g/m

2)

Feed (kg/month)

0

10

20

30

40

50

60

70

80

90

100

0 500 1000 1500 2000

% A

lgal

co

ver

Ru

sse

ll si

te 5

Feed (kg/month)

0

10

20

30

40

50

60

70

80

90

100

0 500 1000 1500 2000

% A

lgal

co

ver

Ru

sse

ll si

te 7

Feed (kg/month)

Figure 26. Absence of relationship between spot benthic algal chlorophyll-a and % cover values

and monthly feed inputs for sites 5 and 7 in the Russell River.

32

Benthic invertebrates

Results of both quantitative (surber) and AUSRIVAS rapid assessment sampling of benthic invertebrates are shown in Tables 2 to 5. Densities and taxon richness (‘diversity’) observed from quantitative samples were high at all sites on both sampling occasions in 2014/15. There was no decline in either diversity or total abundance between site 3 and sites 5 or 7. Total abundance increased at the downstream sites. Several taxa markedly increased in abundance (by a factor of two) at site 7 in spring 2014 relative to site 3 (Table 2), while a number of taxa had higher abundances at both sites 5 and 7 than at site 3 in autumn 2015. Many of these taxa were water-quality sensitive families, indicating that while densities increased, presumably due to higher in-stream productivity, there was also no evidence of changes in water quality causing any negative impacts. Values for AUSRIVAS O/E scores and for EPT scores are shown in Figure 27 for the four sites (1, 3, 5 and 7) in the Russell. No substantive change in these scores was observed for sites 5 or 7 when compared to site 3 on either occasion in 2014/15, as had been observed in 2008. In addition for either the O/E or EPT indicators there is no substantive difference in values for 2014/15 and 2008, with all values falling in the reference range (Figure 27). These results indicate that the observed changes in algal biomass and cover downstream of the HAC outfall are not associated with any decline in macroinvertebrate diversity, or any major change in community composition other than increases in abundance presumably related to increased instream productivity. It also implies that while the HAC facility is causing an elevation in nutrient levels, this is not causing the type of substantive impacts normally associated with organic pollution and/or low dissolved oxygen that have been observed for other nutrient-rich wastewater outfalls (Davies pers. obs.).

33

Table 2. Macroinvertebrate faunal data from quantitative (surber) sampling of riffle habitat at sites 3, 5 and 7 in the Russell River in spring (November) 2014. (Numbers = n per 0.22 m2 of stream

bed, i.e. 20% subsample of 12, pooled Surber samples each of 0.09 m2 stream bed area). For

beetles (Coleoptera), A = adult form, L = larval form. Numbers in bold italics indicate taxa with substantial abundance increases relative to the

upstream reference site 3.

21/11/2014 Site 3 Site 5 Site 7

20% of 12 surbers

Upstream HAC intake Downstream HAC outfall Lorkins Brdge

Class Order Family Sub family

Platyhelminthes Turbellaria

4 3 7

Annelida Oligochaeta

37 36 69

Arachnida Acarina

7 6 13

Insecta Plecoptera Eustheniidae 74 66 121

Austroperlidae 2 1 3

Gripopterygidae 112 101 197

Notonemouridae 4 4 8

Ephemeroptera Leptophlebiidae 82 72 141

Baetidae 63 46 95

Odonata Telephlebiidae 2 2 4

Diptera Chironomidae: Chironominae 10 9 18

Chironomidae: Orthocladiinae 755 752 1506

Chironomidae: Podonominae 11 4 13

Chironomidae: Tanypodinae 1 1 2

Chironomidae: Diamesinae 29 27 56

Simuliidae 18 13 29

Tipulidae 3 1 4

Athericidae 1 1 1

Empididae 4 4 7

Dip. Unid. Pup. 23 20 42

Trichoptera Calocidae 2 1 3

Conoesucidae 25 25 48

Glossosomatidae 1

1

Helicopsychidae 17 14 28

Hydrobiosidae 31 29 58

Hydropsychidae 37 29 56

Hydroptilidae 335 335 663

Leptoceridae 45 42 85

Philopotamidae 2 2 4

Philorheithridae 4 4 7

Trich. Unid. Pup. 9 9 18

Coleoptera Elmidae A 45 32 70

Elmidae L 57 55 108

Scirtidae L 2 1 3

Psepheniidae L 13 10 21

N Taxa 35 34 35

Total abundance 1867 1757 3509

34

Table 3. Macroinvertebrate faunal data from quantitative (surber) sampling of riffle habitat at

sites 3, 5 and 7 in the Russell River in autumn (March) 2015. (Numbers = n per 0.22 m2 of stream

bed, i.e. 20% subsample of 12, pooled Surber samples each of 0.09 m2 stream bed area). For

beetles (Coleoptera), A = adult form, L = larval form.

Numbers in bold italics indicate taxa with substantial abundance increases relative to the

upstream reference site 3.

19/03/2015 Site 3 Site 5 Site 7

20% of 12 surbers

Upstream HAC intake Downstream HAC outfall Lorkins Brdge

Class Order Family Sub family

Platyhelminthes Turbellaria

1 8 3

Bivalvia Sphaeriidae

Mollusca Gastropoda Hydrobiidae 1

Planorbidae

2

Gastr. Unid.

3

Annelida Oligochaeta

11 12 30

Arachnida Acarina

1 6

Crustacea Ostracoda

2

Insecta Plecoptera Eustheniidae 16 6 6

Austroperlidae 5

3

Gripopterygidae 6 16 2

Notonemouridae

1

Ephemeroptera Leptophlebiidae 36 68 108

Baetidae 27 80 48

Odonata Telephlebiidae 1

Hemiptera Corixidae

1

Diptera Chironomidae: Chironominae 26 12 34

Orthocladiinae 11 17 57

Podonominae

1

Simuliidae

2 1

Tipulidae 1 7 1

Athericidae 3

Empididae 1 1 6

Dip. Unid. Pup. 6 3 5

Trichoptera Calocidae 5 8 3

Conoesucidae 3 29 2

Glossosomatidae 2

Helicopsychidae 6 7 5

Hydrobiosidae 3 6 10

Hydropsychidae 25 60 30

Hydroptilidae

2

Leptoceridae 7 28 31

Philorheithridae 8 22 7

Trich. Unid. Pup.

2

Coleoptera Elmidae A

4 5

Elmidae L 13 26 67

Scirtidae L 14 23 41

Psepheniidae L 4 13 1

N Taxa 27 29 27

Total abundance 244 468 515

35

Table 4. Macroinvertebrate faunal data from rapid assessment (AUSRIVAS) sampling of riffle

habitat at sites 3, 5 and 7 in the Russell River in spring (November) 2014. (Numbers = n per sample,

live-picked). For beetles (Coleoptera), A = adult form, L = larval form.

Values derived from these samples of the AUSRIVAS O/E index (and impairment band) and the EPT

index are also shown.

21/11/2014 Site: Site 3 Site 5 Site 7

River: Upstream HAC intake Downstream HAC outfall Lorkins Bridge

Sample: RAP 1 RAP 2 RAP 1 RAP 2 RAP 1 RAP 2

Class Order Family Sub family

Annelida Oligochaeta

3 6 1 1

Arachnida Acarina

3 2 1 2

3

Insecta Plecoptera Eustheniidae 32 30 15 12 6 12

Austroperlidae 1 1 1

Gripopterygidae 9 2 11 14 3 1

Ephemeroptera Leptophlebiidae 38 47 22 23 34 30

Baetidae 27 26 6 12 5 8

Diptera Chironomidae: Chironominae 2 1 2 1

Chironomidae: Orthocladiinae 4 77 60 4 2

Chironomidae: Podonominae 2 3

Chironomidae: Diamesinae 16 12 2 1

Simuliidae 3 4 1 1

1

Tipulidae 1 3 3 2

Athericidae 1 1

Empididae 1

Dip. Unid. Pup. 1 3

Trichoptera Calocidae 1 1 1

Conoesucidae 2 4 10 12 2 6

Ecnomidae 1

Glossosomatidae 1

Helicopsychidae 1 5 12

Hydrobiosidae 10 6 19 28 25 15

Hydropsychidae 5 4 4 24 8 28

Hydroptilidae 7 6 6 5 9 7

Leptoceridae 6 2 2 3 34 19

Philopotamidae 1 1

6

Philorheithridae 2 2 10 6

Trich. Unid. Pup. 1 3

Coleoptera Elmidae A 5 4 8 8 40 22

Elmidae L 1 1 1

3

Scirtidae L 1 4

Psepheniidae L 3 3 2 1 2 7

N Taxa By sample 24 21 22 19 21 23

Mean 22.5 20.5 22

O/E By sample 1.14 0.99 1.05 0.95 1.00 1.10

Mean 1.07 1.00 1.05

Band A A A

EPT ratio By sample 0.50 0.52 0.64 0.58 0.62 0.57

Mean 0.51 0.61 0.59

36

Table 5. Macroinvertebrate faunal data from rapid assessment (AUSRIVAS) sampling of riffle

habitat at sites 3, 5 and 7 in the Russell River in autumn (March) 2015. (Numbers = n per sample,

live-picked). For beetles (Coleoptera), A = adult form, L = larval form.

Values derived from these samples of the AUSRIVAS O/E index (and impairment band) and the EPT

index are also shown.

19/03/2015 Site: Site 3 Site 5 Site 7

River: Upstream HAC intake Downstream HAC outfall Lorkins Bridge

Sample: RAP 1 RAP 2 RAP 1 RAP 2 RAP 1 RAP 2

Class Order Family Sub family

Mollusca

Planorbidae 1

Annelida Oligochaeta

6 6 1

4

Arachnida Acarina

4 1 2 1 6 3

Insecta Plecoptera Eustheniidae 32 21 19 26 11 29

Austroperlidae 2 2 1

Gripopterygidae 1 1 6 1 2

Ephemeroptera Leptophlebiidae 13 31 17 20 25 43

Baetidae 48 58 10 19 11 24

Odonata Telephlebiidae 4 1 1

Hemiptera Veliidae

1

Notonectidae 1

Diptera Chironomidae: Chironominae 8 6 1 1 13 3

Orthocladiinae 2 1 10 8 11 8

Podonominae 1 1

Simuliidae 1 1 1

Tipulidae 2 2 1

1

Athericidae 1

Dip. Unid. Pup.

1

Trichoptera Calocidae 1 1 2 4

Conoesucidae 1 1 15 4 6 2

Glossosomatidae 1

Helicopsychidae 5 3 2

Hydrobiosidae 7 7 21 14 21 38

Hydropsychidae 38 5 47 87 43 32

Leptoceridae 13 4 21 24 40 38

Philorheithridae 4 11 15 18 9

Trich. Unid. Pup. 2 2

1

Coleoptera ElmidaeA 7 2 5 1 18 4

ElmidaeL 2 1 5 1 6

ScirtidaeL 7 6 8 7 16 17

PsepheniidaeL 5 3 5 10 3 6

N Taxa By sample 21 19 22 25 20 21

Mean 20 23.5 20.5

O/E By sample 1.04 0.89 0.95 0.90 0.90 1.00

Mean 0.97 0.92 0.95

A A A

EPT ratio By sample 0.48 0.53 0.55 0.48 0.60 0.48

Mean 0.50 0.51 0.54

37

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 1 2 3 4 5

Sco

re

km

O/E 2008

O/E 2014

O/E 2015

0.0

0.2

0.4

0.6

0.8

0 1 2 3 4 5

Sco

re

km

EPT 2008

EPT 2014

EPT 2015

Figure 27. Benthic macroinvertebrate condition scores for the Ausrivas O/E and EPT indicators for

sites 1, 3, 5 and 7 in the Russell River against distance from Russell Rd bridge in autumn 2008,

spring 2014 and autumn 2015.

Horizontal dashed lines indicate the lower bounds for the ‘unimpaired’ score ranges:

upper plot, for O/E (defining the unimpaired or ‘A’ AUSRIVAS reference band);

lower plot, for TRCI ‘unimpaired’ EPT scores (NRM South 2009).

38

Fish

Five species were caught in total across the two surveys, four in spring 2014 and five in autumn 2015 (Table 6). The fish assemblage was numerically dominated by brown trout (Salmo trutta), followed by the native Sandy (Pseudaphritis urvillii). Both species had their highest density at site 5 on both sampling occasions. A range of size classes were observed for these two species which are maintaining a self-sustaining population in the river. No fish showed signs of poor condition or disease. The high density in the reach at site 5 suggests that elevated food productivity at this site is sustaining higher fish productivity. The high density at this site also suggests that water quality is good in this reach. The lower densities at sites 3 and 7 are typical of the densities observed in similar sized streams elsewhere in southern Tasmania, though a degree of fishing pressure may be occurring at Lorkins Bridge, which would lead to lower adult fish densities there. Table 6. Fish species and abundance observed in standardised surveys of three sites in the Russell

River in November 2014 and March 2015. N = numbers caught per 20 minutes battery-on time.

Date, Site 3 Site 5 Site 7

Common name Scientific name Age class Upstream HAC intake Downstream HAC outfall Lorkins Bridge

21/11/2104

Brown trout Salmo trutta adults 8 8 2

juveniles

1

Sandy Pseudaphritis urvillii all 5 13 8

Mountain galaxias Galaxias truttaceus "

Blackfish Gadopsis marmoratus "

1

Shortfin eel Anguilla australis " 1 1 5

19/03/2015

Brown trout Salmo trutta adults 6 10 3

juveniles

1

Sandy Pseudaphritis urvillii all 5 30 12

Mountain galaxias Galaxias truttaceus "

1

Blackfish Gadopsis marmoratus "

1

Shortfin eel Anguilla australis " 2

39

Discussion During the period March 2008 to April 2015, water discharged from the Huon Aquaculture Company

(HAC) farm in the Russell has continued to chronically raise nutrient (N and P) levels in the Russell

downstream of the discharge location. The main outfall upstream of site 5 continues to be

associated with raised nutrient concentrations and that this raises them above recommended

threshold levels which lead to elevated benthic algal growth for this site.

Five pieces of evidence continue to support the hypothesis that raised algal density and cover in the Russell River in the reach immediately downstream of the HAC outfall are caused by the elevation in nutrient levels: 1. The physical location and spatial pattern of a stepped increase in algal levels being associated with the location of the HAC outfalls, which also cause river nutrient levels to be raised. It should be noted that there is evidence for greening (visual score) of a small tributary adjacent to site 5 which is not directly influenced by the hatchery to levels comparable to site 5. 2. The positive correlations between averaged algal levels and nutrient concentrations across the entire data set. 3. The positive correlation between algal chlorophyll-a and algal cover at site 5, with a weaker correlation at site 7 and no such correlation at sites 1 and 3. 4. The positive correlations between changes in chlorophyll-a between site 3 and site 5 and the corresponding changes in dissolved reactive phosphorus (not observed for site 7). 5. Nutrient levels in the Russell River falling within published ranges within which stream algal growth is known to be enhanced (see Davies and Cook 2009). It is therefore concluded that the algal levels in this reach of the Russell River are caused by raised nutrient levels derived from discharge of HAC wastewater (or a neighbouring and as yet unknown source), noting that there appears to be no significant relationship between flow-through farm feed inputs and algal levels at ether site 5 or site 7 in the reaches downstream of the wastewater outfall. Several new observations touch on the relationship between raised algal levels at Lorkins Bridge (site 7) and upstream causal factors: 1. a positive correlation between temporal changes in chlorophyll-a levels at site 7 and at sites 3

and 1 (describing 30% of the variance in site 7 chlorophyll levels), but not site 5; 2. the weak correlation between chlorophyll-a levels at site 7 and site 5; 3. a significant correlation between levels of algal cover at sites 5 and 7; 4. observation of higher algal levels at site 7 than at site 5 on many occasions between 2008 and

2015; 5. no correlation between changes in algal cover with time at site 7 and sites 3 or 1 - also observed

for site 5; 6. mean and median chlorophyll-a and % cover at site 7 have tended to increase with time relative

to those at site 5. These observations indicate that algal levels at Lorkins Bridge (site 7) are driven by a combination of causes, only one of which is the influence of the HAC outfall. It appears that algal biomass (measured as chl-a) is largely controlled by ‘natural’ stream factors such as flow events and/or changing light conditions, while algal cover is partially driven by the influence of the HAC discharge with a possible additional driver. The potential for other nutrient sources to drive some of the changes in benthic algae at Lorkins Bridge cannot be discounted. An interim management threshold of 30 mg/m2 algal chlorophyll-a was recommended, along with a

set of mean nutrient concentration thresholds which we believe should reduce the risk of high algal

40

levels. An upper limit of 1000 kg feed per month was proposed on a trial basis, noting that inputs

may have to be reduced further (to below 800 kg) if high algal levels occur and persist. This limit was

exceeded on occasion, and the 800 kg threshold exceeded frequently since 2008.

This raises the issue of whether the feed limit should both be properly enforced and reduced to at

least 800 kg per month – and without High P supplementation. If the management aim is to reduce

algal density in the Russel downstream of the HAC facility, and since site 7 appears to be strongly

influenced by some of the same influences experienced by site 5, at least in terms of algal cover – it

would appear logical to make this further adjustment to the feed input and to ensure that it remains

in place for another period of monitoring.

It should be noted that benthic algae are a fundamental component of river systems, including those

in Tasmania. Varying levels of algal biomass and cover are common with time and location within

Tasmanian streams, and management should focus on achieving acceptable levels, rather than

eliminating the visible presence of algae. It is also important to note that levels of algae determined

by short term environmental drivers such as average water quality conditions over preceding weeks

to months, preceding flow events and the dominant flow regime, coupled with the level and diurnal

duration of ambient light. In a high energy river such as the Russell River, longer term legacy effects

of preceding nutrient or organic loadings are extremely unlikely and management should focus on

current tor very recent antecedent conditions.

Neither benthic macroinvertebrate community nor the fish assemblage in the Russell downstream of

the HAC outfall show any major signs of stress or decrease in condition. A supplementation of

productivity can be observed at sites 5 and 7 which appears to be driving increases in abundance of

invertebrates and a consequent local increase in fish abundance (especially trout). No declines in

abundance or diversity of water-quality sensitive taxa are evident, several of which have increased in

density at sites 5 and 7 compared to upstream. There therefore appears to have been no major

negative impact of the raised algal levels on the fauna of the Russell River. The overall ecological

impact therefore appears slight. Any management decision with regard to controlling algal density

through management prescriptions at the HAC site should be made in this light.

41

References APHA 2005. Standard Methods For Examination Of Water & Wastewater. 21st edn.

Davies AL and Gee JHR 1993. A simple periphyton sampler for algal biomass estimates in streams.

Freshwat. Biol. 30, 47-51.

Davies PE 2009. Nutrient and Algal levels in the Russell River and their relationship to discharges

from the Huon Aquaculture Company (HAC) farm facility. Report to Huon Aquaculture

Company. December 2009. Freshwater Systems. 40 pp.

DPIW 2008. Conservation of Freshwater Ecosystem Values (CFEV) project Technical Report.

Conservation of Freshwater Ecosystem Values Program. Department of Primary Industries

and Water, Hobart, Tasmania. 227 pp.

DPIW 2008. Site-specific trigger values for physico-chemical indicators monitored under the DPIW

Baseline Water Quality Monitoring Program. Water Assessment Water Quality Report Series,

Report No. WA 08/52. Water Resources Division. Department of Primary Industries and

Water, Hobart, Tasmania.

NRM South 2009. Tasmanian River Condition Index: Methods manual. TRCI project. NRM South,

Hobart.